Nonaqueous electrolyte batteries such as lithium secondary batteries are being actually used in various applications ranging from power supplies in so-called consumer products such as mobile phones and notebook computers, to drive power supplies for vehicles such as automobiles. There have recently been increasing demands on higher performances for the nonaqueous electrolyte batteries. In particular, enhancements are desired in various battery characteristics such as high capacity, low-temperature service characteristics, high-temperature storage characteristics, cycle characteristics and overcharge safety.
Electrolytic solutions used in the nonaqueous electrolyte batteries are usually composed of electrolytes and nonaqueous solvents as the main components. Examples of the main nonaqueous solvents include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; and cyclic carboxylate esters such as γ-butyrolactone and γ-valerolactone.
A number of studies have been carried out on nonaqueous solvents, electrolytes and additives in order to enhance characteristics of nonaqueous electrolyte batteries such as load characteristics, cycle characteristics, storage characteristics and overcharge safety.
Patent Literatures 1 to 3 propose that various aromatic compounds such as cyclohexylbenzene are added to electrolytic solutions, and this method achieves a certain level of enhancements in overcharge safety and durability.
Patent Literatures 4 and 5 propose that a quaternary carbon compound which has a tertiary alkyl group bonded directly to a phenyl group, for example, 2,2-diphenylpropane, is added to an electrolytic solution in order to satisfy both cycle characteristics and overcharge safety of nonaqueous electrolyte secondary batteries.
Patent Literatures 6 to 8 propose that compounds such as tert-butylbenzene and tert-pentylbenzene are added to electrolytic solutions for nonaqueous electrolyte secondary batteries.